Conventionally, there is known a blower used in a ceiling built-in ventilating fan as this type (refer to patent literature 1, for example).
Hereinafter, a description is made of such a blower referring to FIG. 9, which is a sectional side view showing a conventional blower.
As shown in FIG. 9, blower 101 includes frame 102, casing 105, fan 106, motor 107, top plate 108, and adaptor 112. Here, casing 105 is spiral and has casing inlet 103 drawing outside air into frame 102 and casing outlet 104 blowing out air. Fan 106 sends air from casing inlet 103 to casing outlet 104. Motor 107 rotarily drives fan 106. Top plate 108 fixes casing 105 with motor 107. Adaptor 112 has adaptor inflow opening 109 communicating with casing outlet 104 and duct connection opening 111 for blowing out air toward duct 110.
Casing outlet 104 has a rectangle cross section. The cross-section shape changes from a rectangle to a round shape from adaptor inflow opening 109 to duct connection opening 111.
In such a conventional blower, air passes through inside adaptor 112 over a short distance. Further, the cross-section shape sharply changes from the rectangle of adaptor inflow opening 109 to the round shape of duct connection opening 111. This decreases the blowing efficiency due to pressure loss in an air flow from fan 106 and generates noise due to turbulent flows.